Safety device for pressure vessels, particularly of the type associated with nuclear reactors

ABSTRACT

As a safety measure relating to pressure vessels of nuclear reactors, there is provided a safety tank surrounding the pressure vessel at least in its upper range and a guard ring overlapping the upper edge of the safety tank. The guard ring is disconnectably secured by means of bolts extending within the safety tank to a carrier ring situated under the nipples of the pressure vessel.

United States Patent Schabert Nov. 27, 1973 SAFETY DEVICE FOR PRESSUREVESSELS, PARTICULARLY OF THE TYPE ASSOCIATED WITH NUCLEAR REACTORSHans-Peter Schabert, Erlangen, Germany Siemens Aktiengesellschaft,Berlin and Munchen, Germany Filed: Sept. 3, 1971 Appl. No.: 177,552

Inventor:

Assignee:

Foreign Application Priority Data Sept. 8, l970 Germany P 20 44 304.3

US. Cl 176/87, 52/249, 176/38, 220/3, 220/9 A Int. Cl. G2lc 13/00 Fieldof Search 176/87; 220/3, 9 A; 52/249 References Cited UNITED STATESPATENTS 5/l97l Fletcher 176/87 3,121,046 2/1964 Trickett et al. 176/873,438,857 4/1969 Sulzer 176/87 3,367,839 2/1968 Chinaglia... 176/873,182,000 5/1965 Benzler 176/87 2,983,659 5/l96l Treshow 176/87 PrimaryExaminer-Reuben Epstein Attorney-Edwin E. Greigg [5 7] ABSTRACT As asafety measure relating to pressure vessels of nuclear reactors, thereis provided a safety tank surrounding the pressure vessel at least inits upper range and a guard ring overlapping the upper edge of thesafety tank. The guard ring is disconnectably secured by means of boltsextending within the safety tank to a carrier ring situated under thenipples of the pressure vessel.

20 Claims, 3 Drawing Figures SAFETY DEVICE FOR PRESSURE VESSELS,PARTICULARLY OF THE TYPE ASSOCIATED WITH NUCLEAR REACTORS BACKGROUND OFTHE INVENTION Due to the increasing size in the pressure vessels ofnuclear reactors and due to the tendency of establishing, in anincreasing number, nuclear reactors in or in the vicinity of denselypopulated areas, in designing safety measures for the nuclear reactors,accidents due to a sudden rupture of the reactor pressure vessel have tobe given prime consideration.

In this connection a number of measures have already been proposed.Thus, for example, according to one proposal, the cover of the reactorpressure vessel is held in place, even in case of the rupture of all thesecuring bolts, by virtue of a securing structure or a second securingcover. Such safety structures, however, offer protection only againstthe rupture of the reactor cover and not against a rupture of thepressure vessel proper. Further, the aforenoted securing devices arevoluminous and heavy to such an extent that their manufacture andshipment present extraordinary difficulties.

OBJECT, SUMMARY AND ADVANTAGES OF THE INVENTION It is an object of theinvention to provide an improved safety device for the aforenotedpurpose which requires relatively small work and material input andwhich protects in a secure manner against a rupture of at least the mostendangered portions of a pressure vessel.

Briefly stated, according to the invention, there are provided a safetytank surrounding at least the upper range of the pressure vessel and aguard ring overlapping the bolts of the pressure vessel and the upperedge of the safety tank. The guard ring is disconnectably secured to asupport mechanism disposed under the inlet and outlet nipples of thepressure vessel by means of tightening members extending inside thesafety tank.

Thus, the particularly endangered portion of the pressure vessel issurrounded by a safety tank, whereby an increased protection is providedagainst components that may be hurled outwardly upon a rupture of thepressure vessel or the cover bolts and also, the outflow rate of thecoolant is limited. Furthermore, by providing the guard ring and thetightening members (which may be formed as tension bolts) inside thesafety tank, the bending moment is reduced, because the diameter of thecircle along which the bolts for the guard ring are disposed, is smallerthan the upper portion of the safety tank.

The invention will be better understood as well as further objects andadvantages become more apparent from the ensuing detailed specificationof a preferred, although exemplary, embodiment of the invention taken inconjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic longitudinalsectional side elevational view of a pressure vessel incorporating thepreferred embodiment of the invention;

FIG. 2 is a sectional view along line 11-11 of FIG. 1 and FIG. 3 is atop plan view of the pressure vessel incorporating the preferredembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the Figures, thepressure vessel 1 proper of the nuclear reactor comprises a sphericallyarcuate cover 2 and a cylindrical lower part 3 provided with inlet andoutlet nipples 4 to which there are connected tubular conduits 24 forthe introduction and withdrawal of the reactor coolant. The pressurevessel 1 is surrounded by a concrete cylinder 5 which serves as abiological shield. According to the invention, the pressure vessel 1 isat least at its upper range surrounded at a predetermined distance by asafety tank 6, l l, the internal diameter of which, for facilitatingassembly, is expediently somewhat greater than the greatest diameter ofthe pressure vessel 1 measured across the coolant nipples 4. Above thepressure vessel bolts 10 there is arranged a guard ring,7 which overlapsthe bolts 10 and the upper edge of the safety tank 6 11. The guard ring7 is disconnectably secured by tightening means formed of bolts 8extending within the safety tank 6, 11 to a carrier ring 9 situatedunder the nipples 4. Expediently, the bolts 8 are downwardly andoutwardly divergent from the longitudinal axis of the assembly. It isalso feasible to anchor the bolts 8 directly in the concrete cylinder 5.

It is noted that the guard ring 7 is designed so that a cross sectionalportion thereof with more than half of the bending resistance issituated within the circle along which the bolts are disposed. In thismanner the guard ring 7 may be of reduced weight while being able towithstand the same loads.

For the purpose of reducing the shipping weight of the safety tank andfor facilitating its handling at the construction site, the upper partof the safety tank 6, 1 1 is expediently made of a loosely positionedcylindrical casing 11 which may be tightened to the guard ring 7 so thatit is removable therewith as a unit. The mid portion 6 of the safetytank 6, 11 may sit loosely on the carrier ring 9 or may be fixedlyattached thereto. It is noted, however, that it is feasible to make thesafety tank 6, 11 as a single cylindrical component.

It may be further advantageous to provide over the vessel cover 2 aguard cover 12 held down by the guard ring 7. For example, in boilingwater reactors, the guard cover 12 may be made as one piece with theguard ring 7, or in pressurized water reactors it may be supportedseparately and provided with openings 13 for the control bar guides 14.It may be advantageous if the guard cover 12 extends only over the areainside the circle along which the bolts 10 are located to permit itsremoval together with the vessel cover 2. Further, between the guardcover 12 and the pressure vessel cover 2 there may be provided a freespace constituting an overflow clearance 15.

In order to prevent damaging of the clamping bolts 8. and the outersafety tank 6, 11 by flying debris upon rupture of the pressure vessel,the freedom of motion of the vessel debris may be substantially limitedby means of inserted filler components 17 which are inserted from abovebetween the pressure vessel 1 and the safety tank 6, 11 and which may bemade of cast iron or heavily reinforced or steel-clad concrete blocks.

For the protection of the lower portion of the pressure vessel 1 aswell, the latter may be surrounded by a lower safety tank part 18 whichmay be in a close contacting relationship with the pressure vessel 1 or,for

permitting the performance of repetition tests, it may be situatedspaced therefrom. In order to limit the impact effect of the flyingdebris in case of a spacedly arranged safety tank part 18, it isadvantageous if the intermediate space between the component 18 and thepressure vessel 1 below the carrier ring 9 is filled with a steel ribstructure 19. The carrier ring 9 may be fixedly connected with the lowersafety tank part 18 as shown in FIG. 1.

The individual components of the safety tank, including the guard cover12, may be made of a simple ductile steel in the shape of sheets or caststeel rings. The safety tank components 18 and 6, as well as the guardring 7 and the guard cover 12 are provided at their outer side with aninsulation 20, so that the safety tank reaches approximately the reactortemperature whereby its ductility is substantially increased. The amountof radiation is, by virtue of the shielding effected by the pressurevessel proper so small that an embn'ttlement does not occur.

It is, however, feasible to omit the steel lower part 18 of the safetyvessel without thereby eliminating the protection of the pressure vesselin its lower range. Such a result is achieved by designing the concretecylinder as a concrete pressure container. In such a case the carrierring 9 is either secured to, or embedded in the concrete cylinder 5, orits function is taken over by the concrete pressure container itself insuch a manner that the tightening bolts 8 transmit their forces to theaxial tensioning member or reinforcing means, as the case may be.

In order to prevent a displacement of the pressure vessel 1 inside theconcrete cylinder 5 in case of a rupture, it is expedient to support thepressure vessel 1 not only by claws 16 which engage the carrier ring 9and the pressure vessel 1 below the nipples 4, but also by additionalhigh-strength supports 23 which are situated below the pressurevessel 1. In case of a transversal rupture, the liberated axial forcesare taken up by these lower, circumferentially extending supports 23. Inthe presence of these measures, any shift in the pressure vessel 1 is sosmall that the core carrying structure and thus the reactor core are notsignificantly deformed. The safety tank is so designed that it resiststhe saturation vapor pressure in the hot branch of the reactor coolant.In the instant immediately following a rupture, the higher operationalpressure of the reactor immediately drops due to the fact that a smallquantity of elastically compressed water escapes through the overflowclearance between the cover 2 of the pressure vessel 1 and the guardcover 12. In order to further prevent that in case of a rupture in thepressure vessel, the outflow rate of the coolant in the range of themain coolant nipples 4 is unpermissibly high, the corresponding outflowpassage sections may be decreased by piston rings 21 which, in anemergency, may shift with the associated nipples.

If the reactor fuel has to be replaced, the guard ring 7 is lifted outas a unit with the associated cylindrical casing 11 of the safety tankand the associated insulation 20, together with the upper filler stones17. If a guard cover 12 is present in the structure, it remainspositioned on the reactor cover 2. During repetition tests, the guardcover 12 may be either lifted only about 40 centimeters upwardly or,after assembling the control rod drive means 14, may be entirelyremoved. Additionally, the filler stones 17 in the range of the nipples4 are taken out to permit a removal of the bolts 8 of the guard ring 7.The repetition test of the lower spherical bottom of the pressure vessel1 occurs, in case the lower portion 18 of the safety tank is situated ina spaced manner, from the outside with the aid of a particular devicethrough a pressure-resistant oblique conduit 22 which passes through thebiological shield 5 and the safety tank portion 18.

By means of the aforedescribed safety device in the form of a safetytank which entirely or partially surrounds the pressure vessel proper,the consequences of a rupture in the reactor pressure vessel may besubstantially suppressed in a simple manner.

It is to be understood that the basic principle of the invention mayalso find application in other pressure vessels, where the cover isarranged laterally or at the base and which serve for storing a materialunder high pressure.

What is claimed is:

1. In a safety device for a pressure vessel, the latter includingcircumferentially arranged inlet and outlet nipples and a removablecover secured to the pressure vessel by cover bolts arranged along acircle, the improvement comprising A. a safety tank spacedly surroundingat least an upper terminal portion of said pressure vessel including therange of said nipples, said safety tank being normally isolated from thepressure prevailing in said pressure vessel, said safety tank having anupper edge,

B. a guard ring essentially overlapping said upper edge of said safetytank and said cover bolts,

C. a support means surrounding said pressure vessel below said nipplesand C. tightening members disconnectably fastening said guard ring tosaid support means, said tightening members being arranged along acircle and extending within said safety tank.

2. An improvement as defined in claim 1, wherein the cross section ofsaid guard ring is such that more than one half of its bendingresistance is within the circle along which said tightening means aredisposed.

3. An improvement as defined in claim 1, wherein the upper portion ofsaid safety tank is formed of a cylindrical casing loosely sitting on amid portion of said safety tank and being directly affixed to said guardring.

4. An improvement as defined in claim 1, wherein said tightening membersassociated with said guard ring are outwardly divergent.

5. An improvement as defined in claim 4, wherein said tightening membersare formed as tension bolts.

6. An improvement as defined in claim 1, including a guard coversituated above said removable cover within the circle along which saidcover bolts are arranged, said guard cover including an outer marginalrange overlapped by said guard ring.

7. An improvement as defined in claim 6, wherein said guard ring andsaid guard cover constitute a jointly removable unit.

8. An improvement as defined in claim 1, wherein said support means isformed as a carrier ring.

9. An improvement as defined in claim 8, including a concrete cylindersurrounding said pressure vessel and formed as a concrete pressurecontainer, said carrier ring being embedded in said concrete cylinder.

10. An improvement as defined in claim 1, including a concrete cylindersurrounding said pressure vessel and formed as a concrete pressurecontainer, said tightening means being directly anchored in saidconcrete cylinder.

11. An improvement as defined in claim 1, including a safety tankportion surrounding said pressure vessel below said nipples and belowsaid support means.

12. An improvement as defined in claim 11, wherein said safety tankportion is in a face-to-face engagement with said pressure vessel.

13. An improvement as defined in claim 11, wherein said safety tankportion spacedly surrounds said pressure vessel, said improvementincludes a steel rib structure at least partially filling the spacebetween said safety tank portion and said pressure vessel below saidsupport means.

14. An improvement as defined in claim 1, wherein said support means isformed as a carrier ring constituting one part of said safety tank.

15. An improvement as defined in claim 11, wherein said support means isformed as a carrier ring constituting one part of said safety tankportion.

16. An improvement as defined in claim 1, including removable protectivefiller members disposed in the range of said tightening members betweensaid safety tank and said pressure vessel on the one hand and said guardring and said support means on the other hand.

17. An improvement as defined in claim 6, including a safety tankportion surrounding said pressure vessel below said nipples and belowsaid support means; said safety tank, said safety tank portion, saidguard ring and said guard cover are provided with external insulatingmeans.

18. An improvement as defined in claim 6, including an overflowclearance provided between said vessel cover and said guard cover.

19. An improvement as defined in claim 1, including A. a concretecylinder surrounding said pressure ves sel,

B. a safety tank portion surrounding said pressure vessel below saidnipples and below said support means and C. a pressure-resistant obliqueconduit passing through said concrete cylinder and said safety tankportion and merging into the space below said pressure vessel.

20. An improvement as defined in claim 1, including additional supportmeans engaging lower outer portions of said pressure vessel.

1. In a safety device for a pressure vessel, the latter includingcircumferentially arranged inlet and outlet nipples and a removablecover secured to the pressure vessel by cover bolts arranged along acircle, the improvement comprising A. a safety tank spacedly surroundingat least an upper terminal portion of said pressure vessel including therange of said nipples, said safety tank being normally isolated from thepressure prevailing in said pressure vessel, said safety tank having anupper edge, B. a guard ring essentially overlapping said upper edge ofsaid safety tank and said cover bolts, C. a support means surroundingsaid pressure vessel below said nipples and C. tightening membersdisconnectably fastening said guard ring to said support means, saidtightening members being arranged along a circle and extending withinsaid safety tank.
 2. An improvement as defined in claim 1, wherein thecross section of said guard ring is such that more than one half of itsbending resistance is within the circle along which said tighteningmeans are disposed.
 3. An improvement as defined in claim 1, wherein theupper portion of said safety tank is formed of a cylindrical casingloosely sitting on a mid portion of said safety tank and being directlyaffixed to said guard ring.
 4. An improvement as defined in claim 1,wherein said tightening members associated with said guard ring areoutwardly divergent.
 5. An improvement as defined in claim 4, whereinsaid tightening members are formed as tension bolts.
 6. An improvementas defined in claim 1, including a guard cover situated above saidremovable cover within the circle along which said cover bolts arearranged, said guard cover including an outer marginal range overlappedby said guard ring.
 7. An improvement as defined in claim 6, whereinsaid guard ring and said guard cover constitute a jointly removableunit.
 8. An improvement as defined in claim 1, wherein said supportmeans is formed as a carrier ring.
 9. An improvement as defined in claim8, including a concrete cylinder surrounding said pressure vessel andformed as a concrete pressure container, said carrier ring beingembedded in said concrete cylinder.
 10. An improvement as defined inclaim 1, including a concrete cylinder surrounding said pressure vesseland formed as a concrete pressure container, said tightening means beingdirectly anchored in said concrete cylinder.
 11. An improvement asdefined in claim 1, including a safety tank portion surrounding saidpressure vessel below said nipples and below said support means.
 12. Animprovement as defined in claim 11, wherein said safety tank portion isin a face-to-face engagement with said pressure vessel.
 13. Animprovement as defined in claim 11, wherein said safety tank portionspacedly surrounds said pressure vessel, said improvement includes asteel rib structure at least partially filling the space between saidsafety tank portion and said pressure vessel below said support means.14. An improvement as defined in claim 1, wherein said support means isformed as a carrier ring constituting one part of said safety tank. 15.An improvement as defined in claim 11, wherein said support means isformed as a carrier ring constituting one part of said safety tankportion.
 16. An improvement as defined in claim 1, including removableprotective filler members disposed in the range of said tighteningmembers between said safety tank and said pressure vessel on the onehand and said guard ring and said support means on the other hand. 17.An improvement as defined in claim 6, including a safety tank portionsurrounding said pressure vessel below said nipples and below saidsupport means; said safety tank, said safety tank portion, said guardring and said guard cover are provided with external insulating means.18. An improvement as defined in claim 6, including an overflowclearance provided between said vessel cover and said guard cover. 19.An improvement as defined in claim 1, including A. a concrete cylindersurrounding said pressure vessel, B. a safety tank portion surroundingsaid pressure vessel below said nipples and below said support means andC. a pressure-resistant oblique conduit passing through said concretecylinder and said safety tank portion and merging into the space belowsaid pressure vessel.
 20. An improvement as defined in claim 1,including additional support means engaging lower outer portions of saidpressure vessel.